In the manufacture or processing of viscous materials, such as polymers and other relatively high viscosity substances, it is frequently advantageous to subject the material to reaction, heating, devolatilizing, intimate mixing to achieve uniformity of composition, melt plasticating and the like and, sometimes, to conduct more than one of these operations simultaneously or consecutively in a single apparatus.
Very often the capacity of the processor is determined by the heat transfer or mass transfer to or from the material in process. This material generally moves in rope form advanced by a screw tip as it progresses along the bore wall. It is advantageous to repetitively spread the material and thereafter collect it to provide more surface area for heat and mass transfer while, periodically, subjecting the material to intensive shearing action.
There exists apparatus in the prior art employing eccentrically mounted co-rotating screws; however, these do not treat material in process uniformly. Thus, U.S. Pat. No. 3,288,077 discloses co-rotating screws which are eccentrically mounted, as distinguished from the screws themselves being eccentric in cross-section, which do wipe each other, but there is no screw flight in contact with the bore wall throughout its entire length. Consequently, portions of the bore are not wiped and there is not a uniform treatment of material through the bore as is achieved by this invention.
U.S. Pat. No. 3,717,330 discloses a fully-wiped double cone device in which both the screw elements and the bore walls are fully wiped. However, there is no teaching of multiple tip screws in which one or more of the tips is reserved to spreading the material and thus does not wipe the wall at all.